Cycling UK Forum

I've been given a Tubus rack and I'm pretty sure it's a Luna.

It's as the one here: http://www.petitebikefit.com/luna-racks-by-tubus

The thing is, I don't have the strut connecting it to the brake bridge.

I do have the wee grub screw, but I've tried the arms off my other racks (a Tubus Cargo and a Tortec Ultralite, this is a household of many racks), and they just don't hold firm.

Anyone know where I can get a spare, or can anyone suggest a bodge? It'll be fitted to a bike with mounts on the chainstays, and I noted that Tubus do an adapter for the Fly, but the Luna appears to have been discontinued.

If you can't find exactly what you are after, then I would measure how long a strut you need. assess the mounting options at both ends then look at what SJS has available under rack spares. They have various struts, P-clips and clamps that could be used as a bodge but it may not look pretty!

Dean wrote:they just don't hold firm.

Would a new, possibly longer grub screw with some threadlock be the solution? Grub screws are readily available from e.g. Accu.

My first point would be that the strut on the bike pictured in your link does not look like a standard one which is much shorter. That one looks a lot longer, presumably because it's an a bike with smaller wheels.

If you want a four-point fixing, using the seat stays instead of the brake bolt, I think some sort of improvisation is the only way, perhaps based on this design.

https://www.tubus.com/en/products/acces ... et-for-fly

I presume that fits onto the single strut for three-point fixing, but I'm not clear how it would work.

I had a bike with a Luna rack which is still used by a member of my family so I can have a look to refresh my memory of the exact details, if it would help. I can say with some certainty that the strut supplied wouldn't have worked well with the thing in my link because it would have pushed the rack too far back.

The bike I fitted it to had V brakes so I would have preferred four-point fitting but I'm fairly sure that wasn't an option so I had to go for three.

It looks like the design of the Luna changed at some point from the strut being secured by a grub screw in a hollow tube which was welded to the rest of the rack, to the standard separate detachable clamp unit supplied with other Tubus racks, and the OP appears to have the former.

I think the first priority is to measure the internal diameter of the tube into which the strut is inserted and compare it with the diameter of the Tubus struts on his other bikes. That should indicate whether Tubus supplied a larger diameter strut for the original Luna rack. In other words is the strut a loose fit in the tube?

If the internal diameter is consistant with the current standard struts, the next thing I would check is that the struts tried so far are sufficiently long to enter far enough into the hollow tube and be secured by the grub screw, i.e. it might be necessary to buy a longer Tubus strut if the strut is short and when inserted does not extend fully beyond the grub screw.

the strut will be a standard gauge aluminium tube; the closer the fit of the diameter is, the better it will hold. If for some reason the grub screw is not secure, and you want a more permanent job, the joint can be assembled with epoxy resin. Should this ever need to be disassembled heating to ~150C will render the bond weak and ineffective, and the joint should just pull apart.

You can make a suitable strut by taking some aluminium tube of the correct diameter and doing some (fairly modest) engineering with it.

BTW V brakes do not prohibit four-point racks, but they can sometimes only fit well if you are prepared to fit cranked stays to the upper mounts. Being flexible about your choice of noodle into the rear brake helps too of course.

cheers

I have a Tubus Luna rack and the strut is nominally 8mm OD (measured 7.95mm OD) The internal diameter of the tubing into which it fits is around 8.3mm.Tubus Roundstays are avaialable in various lengths.

All good stuff.

Mine was one of the few bits of cycling kit I've received as a welcome surprise. The rack was reviewed in the CTC mag and I drooled over it. Next news I was the proud owner. The three-point fixing was the only thing which wasn't "just what I wanted" but if an alternative four-point was available, I never sourced one.

Having settled on using three-point, my problem was actually fitting the singles strut. It was straight and had to be curved. I'm ham-fisted and my mechanical fitter son was on the other side of the world but he sent me email instructions on how to use one of his pipe-benders. Then, the end which fitted the chainstay bridge had to be bent 90 degs to fit. I can see why they changed the design and I can guess why your strut is missing. It's not a design for switching bikes.

If you are ok with three-point fitting then I'd check with SJS to make sure theirs are the right dia then bingo! If you want four-point, I can't see any alternative to improvising.

I have a Tubus Luna rack and the strut is nominally 8mm OD (measured 7.95mm OD) The internal diameter of the tubing into which it fits is around 8.3mm.

That's the standard outside diameter for a Tubus Roundstay, so it does suggest to me that the OP's problem is using a Roundstay that is too short.

thirdcrank wrote:my problem was actually fitting the singles strut. It was straight and had to be curved. I'm ham-fisted and my mechanical fitter son was on the other side of the world but he sent me email instructions on how to use one of his pipe-benders. Then, the end which fitted the chainstay bridge had to be bent 90 degs to fit.

Tubus sell two angled brackets for this purpose, and I think the one with the 159 degree bend is supplied as standard with the three point fixing racks.

Tubus even sell a full 'mounting kit' for the Fly rack which includes the bracket and a 240mm Roundstay (as well as the mounting clamp to attach the stay to racks unlike the OP's). I suspect that would probably be the Roundstay length the OP needs, and the Roundstay is offered in 'stainless steel' with that kit to match the rack.

https://www.tubus.com/en/products/accessories-rear-carriers/tubus-product/mounting-knee-for-fly-90

https://www.tubus.com/en/products/accessories-rear-carriers/tubus-product/mounting-knee-for-fly-159

https://www.tubus.com/en/products/accessories-rear-carriers/tubus-product/mounting-set

https://www.bike-components.de/en/tubus/Fly-Mounting-Set-p66079/

slowster wrote: ... Tubus sell two angled brackets for this purpose, and I think the one with the 159 degree bend is supplied as standard with the three point fixing racks.

Tubus even sell a full 'mounting kit' for the Fly rack which includes the bracket and a 240mm Roundstay (as well as the mounting clamp to attach the stay to racks unlike the OP's). ...

That's testimony to Tubus recognising problems and responding to them with solutions. ie Not planned obsolescence but genuine product improvement.

Unless I've misunderstood, the OP is looking for a four-point mounting.

Just ring Lyon - the UK distributor - who are really helpful.

https://lyon.co.uk/cycle/tubus

Enigmadick wrote:Just ring Lyon - the UK distributor - who are really helpful.

https://lyon.co.uk/cycle/tubus

+1 - they also distribute lots of other top kit like Petzl and Ortlieb

I have two bikes with Fly racks, one with the earlier grub-screw fitting (possibly 15 years old now), and one with the current bush design. I think the Luna is similar to the Fly. The connecting rod is available in a variety of lengths, I got a longer one for one of the bikes from SJS Cycles.

The single stay rod can be bent to have a dog-leg to it, so it aligns with mounting points not on the centre line of the bike. Do the bending slowly, and with care to avoid any kinks or over-bending - small amounts of over-bend can be pushed back. I've bent the stays to fit both the racks on our bikes, using a vice (with wood to provide a "soft jaw"), and pushing the stay with bits of timber for leverage. With the low weight carrying design of the Fly, I can't see that the single stay fixing is a limitation.

There is an optional twin-stay fixing pack which should fit either the grub-screw or bush design rack, though I think putting two stays and a bolt in the stay detracts from the elegant appearance and light-weight ethos.

SJS as a source of parts:
https://www.sjscycles.co.uk/rack-spares/?brand=tubus
And within it, the "round stay L" has a variety of lengths.



- Nigel

Thanks everyone, some food for thought. I have been browsing the SJS site for spares, and spotted the adapter for four-point fittings.

I think the arms from my existing racks are a bit too small, and I need one with a diameter just over 8 mm. Or epoxy, as Brucey says.